<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .red {
        background-color: red;
        width: 100px;
        height: 100px;
    }

    .green {
        background-color: green;
        width: 100px;
        height: 100px;
    }
</style>

<body>
    <div class="red"></div>
    <div class="green"></div>
    <div class="red"></div>
    <div></div>
</body>

</html>